The present invention relates to an electronic timepiece, and to a reduction of power consumption in the electronic timepiece by switching a drive pulse width which is applied to a stepping motor in accordance with the load whereby attains a suitable drive and a low power consumption of a stepping motor is attained.
The display mechanism of an analogue type crystal watch heretofore used is generally constructed as shown in FIG. 1. The output of a motor comprising a stator 1, a coil 7 and a rotor 6 is transmitted to a fifth wheel 5, a fourth wheel 4, a third wheel 3 and a second wheel 2. Although not shown the output is then transmitted to a cylindrical member, a cylindrical wheel and a calendar mechanism, whereby a second hand, a minute hand, and hour hand and a calendar are driven.
In the case of wrist watch, a load from the stepping motor is extremely small except for the time for switching the calendar, so that the torque of 10 g/cm in the second wheel is enough for the driving. However, when switching the calendar, the torque of several times higher than this is required. The time required for switching the calendar within twenty-four hours operation is only at most about six hours. However, for the reasons described above in the mechanism according to the prior art, there is a problem that electric power which enables the calendar driving mechanism to be operated in a stable condition must be always supplied from a power supply.
FIG. 2 shows an electronic watch circuit construction according to the prior art. The signal of 32768 KHZ from an oscillation circuit 10 is converted to a one second signal by a frequency dividing circuit. The one second signal is converted to a signal having a 7.8 ms width and a period of 2 seconds by a pulse width combining circuit, and a signal having the same period and pulse width which is dephased by one second are applied to the inputs 15 and 16 of the inverters 13a and 13b.
As a result, an inverted pulse which changes the direction of the current is applied to a coil 14 every one second, so that the rotor 6 magnetized in two poles rotates in one direction. FIG. 3 shows the current waveform thereof. In this manner, the drive pulse width of the present day electronic watch is set by the required maximum torque as its standard. Therefore, in the time interval which does not require a large torque, electric power is wasted. This has prevented the lower power consumption of the watch.